Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  

Go Back   > >

Clydesdales/Athenas (200+ lb / 91+ kg) Looking to lose that spare tire? Ideal weight 200+? Frustrated being a large cyclist in a sport geared for the ultra-light? Learn about the bikes and parts that can take the abuse of a heavier cyclist, how to keep your body going while losing the weight, and get support from others who've been successful.

User Tag List

Thread Tools Search this Thread
Old 08-08-07, 09:31 AM   #1
Thread Starter
Join Date: Jul 2007
Posts: 44
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Tire Pressures

A few tire pressure basics to remember- be careful comparing tire pressures with different size tires! The energy inside a tire is determined by its Pressure times its Volume (P*V). Therefore, for two different tires of the same wheel size, say a 700x23mm compared to a 700x35mm, (P23mm)*(V23mm)=(P35mm)*(V35mm). The volume is proportional to the cross-sectional area of the tire, and so also to the square of the radius of the tire cross section. That way, if we know the ratio of the tire radii squared, we can get an equivalent tire pressure (from an energy standpoint) for two different tires. For the example above, if we have a 35mm tire pressurized to 85 psi, the equivalent 23mm tire would have to have (35mm/2)**2/(23mm/2)**2 *85psi= 197 psi!!! (Conversely, a 23mm tire at 120psi is equivalent to a 35mm tire at 52 psi). The tire pressure is inversely proportional to its volume, so that the larger the volume of the tire, the less pressure is needed to get the equivalent amount of energy. ‘Nuff of the physics lesson- bottom line? Us big guys (and gals) are probably better off with a larger tire at maximum pressure to carry the extra weight, but small enough to get good rolling resistance (which is another physics lesson for another day!).
AeroJoe is offline   Reply With Quote
Old 08-08-07, 09:54 AM   #2
Tom Stormcrowe
Out fishing with Annie on his lap, a cigar in one hand and a ginger ale in the other, watching the sunset.
Tom Stormcrowe's Avatar
Join Date: Mar 2006
Location: South Florida
Bikes: Techna Wheelchair and a Sun EZ 3 Recumbent Trike
Posts: 16,128
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Is it just me, or does BF seem to have a greater proportion of Math and science geeks than the average internet forum? I'm not saying this is a bad thing, by any makes me feel right at home! I'm just askin' is all!

OK, Hijack over and great post, AJ!
. “He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you.”- Fredrick Nietzsche

"We can judge the heart of a man by his treatment of animals." - Immanuel Kant
Tom Stormcrowe is offline   Reply With Quote
Old 08-08-07, 06:12 PM   #3
Bill Kapaun
Senior Member
Bill Kapaun's Avatar
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Bikes: 86 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds.
Posts: 10,098
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 392 Post(s)
I think you forgot to factor in absolute pressure.
Bill Kapaun is offline   Reply With Quote
Old 08-08-07, 06:42 PM   #4
Very Senior Member
MikeR's Avatar
Join Date: Aug 2001
Location: Central Pa
Bikes: 2000 Bianchi San Remo and a mint 1984 Trek 720
Posts: 1,765
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Originally Posted by Bill Kapaun View Post
I think you forgot to factor in absolute pressure.
Don't forget that you yawn to equalize he air pressure behind your ear drums. This slightly changes the air pressure outside your ear drums so you must let a little air out of your tires.
It's better to cycle through life than to drive by it.
MikeR is offline   Reply With Quote
Old 08-08-07, 07:03 PM   #5
Senior Member
DieselDan's Avatar
Join Date: Mar 2003
Location: Beaufort, South Carolina, USA and surrounding islands.
Bikes: Cannondale R500, Motobecane Messenger
Posts: 8,522
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
I just pump to the maximum pressure rating on the sidewall and ride. I paid for these tires, and someone else was paid to come up with the rating.
DieselDan is offline   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

All times are GMT -6. The time now is 07:21 AM.

  • Ask a Question
    get answers from real people!
Click to start entering your question.